Spring retractable rule assemblies have been available commercially for many years. Among the most desirable characteristics commercial rule assemblies can possess is a relatively long total blade length and a relatively compact housing that is of a size and shape, for example, that can easily and comfortably fit in a hand of person using the assembly or that can easily be carried in a pocket or on a belt.
A typical retractable tape rule assembly includes an elongated thin metal rule blade that is mounted on a reel rotatably disposed within a housing assembly. The rule blade is retracted into the housing assembly for storage by coiling it about the reel. In a spring retractable type rule assembly, a coil spring is mounted inside the reel between the reel and a spindle of the housing assembly to provide spring powered rewinding of the blade.
A typical coil spring has a flat ribbon-like metal structure. Spring power is directly related to spring width, thickness and length so that spring power can be increased by increasing any combination of these three dimensions. Increasing spring thickness and/or length, however, requires making the height and length of the housing assembly (i.e., the side dimensions or "footprint") larger. It is particularly important to minimize the footprint of the housing assembly if the same is to be conveniently gripped or carried. Prior art rule blade assemblies used a construction in which the spring width is significantly less than the blade width. When spring power had to be increased in prior art assemblies, spring length and/or particularly spring thickness were increased which tended to make the footprints of prior art housing assemblies relatively large and cumbersome, particularly if blade length was long.
Prior art housing assembly construction also typically used four fasteners located generally in four corners of the housing assembly to secure the housing assembly together. These fasteners were usually four axially extending bolts (where "axial" refers to the direction of the axis of rotation of the reel defined by the spindle). These four fasteners were typically disposed outside of the periphery of the reel. This positioning of the fasteners tends to increase the footprint of the housing assembly. Furthermore, the need for four corners in the housing assembly required that the housing assembly footprint be somewhat square and this square shape is relatively difficult to grasp was one hand.
There is a need for a spring-powered retractable rule assembly having a housing assembly footprint size that is as small as possible for a given blade length and having a footprint with a minimum number of corners and peripherally disposed fasteners to make the housing assembly as easy to hold in a single hand as possible.